Mass spectrometer having a plurality of relatively movable collectors



Aug.14, 1970 RELATIVELY MOVABLE COLLECTORS 2 Sheets-Sheet 1 Filed May16, 1967 1 5 M W OE H mm m w 8 W W mm Av Q Q Q H mm P Wfi m UHIIIIIJ Ill w IJII lluainfliifli mwp A 0Q Ql c 1 m Nm\ om\ United States PatentU.S. Cl. 250-41.9 14 Claims ABSTRACT OF THE DISCLOSURE A massspectrometer is provided with a collector arrangement in whichcollectors are movable relative to one another. Each collector isadapted to receive a portion of the mass spectrum analyzed.

CROSS REFERENCE TO RELATED APPLICATION Mass Spectrometer Sample Movementand Ion Beam Deflector, Ser. No. 638,857, filed May 16, 1967, by PatrickPowers.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to collector structure for mass spectrometers and moreparticularly to a collector structure in which the collectors aremovable relative to one another.

Description of the prior art The present invention is particularlyuseful with spark-source mass spectrometers. In a spark-source massspectrometer, ions of a material to be studied are produced by applyinga high voltage across two electrodes, one or both of which are composedof the sample material, to thereby produce a spark between them. Duringthe period of the spark, ions emanate from the sample material and areaccelerated, for example, by a high voltage accelerating electrode. Theions form an ion beam which is deflected by magnetic and, in so-calleddouble focusing instruments, electrostatic means, and a particularportion of the mass spectrum represented by the ion beam is read as anoutput on a photographic or electric collector.

When analyzing materials with a spark-source mass spectrometer, it hasbeen customary to use photographic detection so that the variations inthe ion beam are averaged out by taking exposures of sufiicient durationon a photographic plate. The accuracy of measuring relativeconcentrations of impurities in some types of sample material isrelatively poor. The range of error may be as much as 20% to 30% ormore.

This inaccuracy results from a number of conditions, one of which is thenon-linear response and uneveness of photographic emulsions.Specifically, the photographic material has an emulsion layer withsilver halide deposited on the surface. It is difiicult to obtain aprecisely uniform distribution of the silver halide and the silverhalide tends to become embedded in the emulsion. Those portions of thesilver halide embedded in the emulsion will not be properly exposed bythe ions and an irregular distribution of the silver halide on thesurface of the emulsion will result in uneven exposures. Photographictechniques present further problems attendant to the difficulties ofinsertion and removal of a photographic plate from the vacuum chamber ofa mass spectrometer before and after exposure.

If electrical detection by known methods is used, then 3,522,428Patented Aug. 4, 1970 only one peak in the mass spectrum can be viewedat a time, and because of the varying nature of the ions produced by thespark, the results of such analysis are usually worse and rarely betterthan with photographic detection.

SUMMARY OF THE INVENTION According to one form of the present invention,electrical detection means in or for a mass spectrometer comprises aseries of ion collectors mounted or mountable at respective positions atwhich they can collect ions in respective different regions of a massspectrum, the collectors being adjustable in position relative to oneanother so that selected ion beams in the mass spectrum may beintercepted by the respective individual collectors.

Each collector is capable of producing an electrical output indicativeof the intensity of the ion beam intercepted by it. More specifically,it is contemplated that the collectors are movably mounted on a plate,each collector being insulated from the other collectors and fromground. The plate upon which the collectors are mounted may bepermanently mountable in the analyzer portion of the mass spectrometeror may be insertable into the analyzer through a vacuum lock in the samemanner as a photoplate. The mounting structure for each collector ispreferably provided with a tongue or other contact means slidablyengaging one of a plurality of stationary output conductors forconveying an electrical signal from the collector out of the evacuatedportion of the mass spectrometer to suitable external amplifiers.

With a permanently-mounted plate within the mass spectrometer, theindividual collectors or collector units could be made adjustable fromoutside the evacuated portion of the mass spectrometer by mechanicalmeans such as the threaded rod arrangement described in the Britishpatent specification No. 957,117, published May 6, 1964, entitledImprovements Relating to Mass Spectrometers. As described in theaforementioned specification, each collector unit may be mounted on aguide rod and a threaded rod, which is rotatable by a shaft extendingthrough a vacuum-tight seal of the mass spectrometer. Rotation of theshaft moves the collector unit along the rods across the paths of theindividual ion beams.

With an insertable and removable plate, it is preferred to adjust therespective positions of the collectors prior to insertion into thecollecting region of the instrument. The respective positions of thecollectors are determined by means of a template which, for example, maybe a previously exposed and developed photoplate or a fluorescent platewith a long decay time.

Employing such arrangements, simultaneous detection of many or all ofthe interesting impurities in a sample may be achieved in a manner whichavoids inherent disadvantages of a photographic plate. It is believedthat the analytical accuracy obtainable with the novel arrangement maywell approach that of instruments employing optical spectroscopy.

Accordingly, an object of the present invention is to provide a noveland improved mass spectrometer and method of operating a massspectrometer for analyzing ions of a sample material with greateraccuracy than by photographic means.

An additional object of the present invention is to provide a novel andimproved mechanism for electrical ion beam detection enabling a massspectrometer to simultaneously produce a number of electrical outputsindicative of the respective intensities of ion beams in differentregions of the mass spectrum.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat schematic sectionalview of a mass spectrometer equipped with the novel collectorarrangement of this invention;

FIG. 2 is a side elevational view of the novel collector arrangement;

FIG. 3 is a bottom view of the arrangement shown in FIG. 2;

FIG. 4 is an enlarged view of one of the collector units as seen fromthe plane indicated by line 4-4 in FIG. 3; and

FIG. 5 is a side elevational view of an alternative form of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a singlefocusing mass spectrometer includes an ion source for producing ions ofmaterial to be analyzed, for example, by developing a high voltage sparkbetween two electrodes, one or both of which is a sample. A suitabletechnique for producing ions is described in the referenced co-pendingapplication of Patrick Powers. The ions are emitted from the ion source10 and accelerated by known techniques and are established alongrespective paths as a plurality of ion beams 11. The ion beams 11 passthrough and are deflected by a magnetic field in a magnetic analyzer 12,the amount of deflection of ions included in an individual ion beamdepending upon the mass of ions included in it. The ion beams 11 aredirected toward a collector arrangement 13 situated in the paths of theion beams 11 within the evacuated portion of the mass spectrometer. Theion beams 11 impinge on respective individual collectors which are apart of the collector arrangement 13, to produce a plurality of outputsindicative of the composition of each respective ion beam.

Referring to FIGS. 2-4, the collector arrangement of one form of thepresent invention generally comprises a support plate 14 having twoelongated entrance slots or tracks 15, 15' aligned end-to-endlongitudinally along the support plate 14 near the top thereof. Theright-hand portion of the collector structure shown in FIGS. 2 and 3 isfragmented, however, it has the same construction as the left-handportion shown in detail. The support plate 14 should be alignedtransversely to the path of travel of the ion beams and should be sooriented that the entrance slots 15, 15 will receive ions over a rangeof the mass spectrum to be analyzed.

The support plate 14 has closely spaced, longitudinally aligned, guideslots or tracks 16, 16. The support plate 14 also has closely spaced,longitudinally aligned, guide slots or tracks 18, 18 arranged parallelto the guide slots 16, 16 respectively. The entrance slot 15 and theguide slots 16, 18 are substantially the same length and are parallel toone another. Similarly, the entrance slot 15' and the guide slots ortracks 16, 18' are substantially the same length and are parallel to oneanother.

A support block 20 is fixed to and extends from the support plate 14 atthe left hand end of the support plate as viewed in FIGS. 2 and 3. Thesupport block 20 is spaced a short distance from the ends of the guideslots 16, 18. Similarly, a support block 22 is fixed to and extends fromthe face of the support plate 14 near its opposite end and is spaced ashort distance from the ends of the guide slots or tracks 16, 18'. Thesupport blocks 20, 22 are preferably composed of an insulating materialsuch as polytetrafluoroethylene (referred to as PTFE), marketed by E. I.Du Pont under the trademark Teflon.

A group of spaced, parallel output conductors 24-29 are spaced from andarranged in a plane parallel to the support plate 14. The outputconductors 24-29 abut the support blocks 20, 22. Clamping blocks 30, 32secure the output conductors 24-29 against the support blocks 20, 22.The clamping blocks 30, 32 are also composed of PTFE and are securedagainst the support blocks 20, 22 to firmly secure the output conductors24-29 by means of clamp screws 34, 36 respectively, located betweenalternate rows of the conductors 24-29.

The collector arrangement shown in FIGS. 2 and 3 includes threecollector units designated generally by the numerals 40, 41, 42supported by the support plate 14. For convenience purposes, only threeunits are shown, however, it is contemplated that the embodiments shownin FIGS. 2 and 3 will include a total of six collector units three shownarranged along the left-hand portion of the support plate 14 and threemore (not shown) arranged along the right-hand portion. It should beunderstood that the present invention is not limited to the use of sixunits, and more or less may be used as desired. All of the collectorunits are identically constructed except for the positioning of outputconnections to the respective output conductors 24-29.

For convenience, only the collector unit 40 shown in detail in FIG. 4will be described in detail. since it is identical to the others. Thecollector unit 40 includes a U- shaped frame 44 which itself includes abody portion 46 aligned normal to the plane of the support plate 14, abase arm portion 47 slidably engaging and parallel to the support plate14 and an upper arm portion 48, partially hidden, spaced from andparallel to the base arm portion 47. The base arm portion 47 includestwo spaced portions 50, 51 which project in opposite directions from thebase arm portion 47. The portions 50, 51, have threaded bores 52, 53 forreceiving screws 54, 55 respectively. The shaft portions of the screws54, 55 pass through and are slidably disposed in the slots or tracks 18,16, respectively, to permit movement of the frame 44 along the supportplate 14 in a path normal to the plane of the drawing shown in FIG. 4and transverse to the path of the ion beam indicated by the arrow Bthrough the entrance slot 15.

A collector mount 60 including a secured portion 61 and a mountingportion 62 is connected to the upper arm portion 48 at the securedportion 61 by means of screws 64. The mounting portion 62 is bent towardthe arm portion 47 to form an obtuse angle with the secured portion 61.The mounting portion 62 includes a depending projection 68 alignedparallel to the body portion 46. A collector plate 70 is connected tothe projection 68.

The mounting portion 62 has a plurality of equally spaced holes 65arranged in a row. A connection in the form of a tongue is mounted onthe mounting portion 62 and secured thereto by screws 91 disposed in theholes 65 at the end of the mounting portion 62 farthest from the bodyportion 46. The connection 90 lies in a plane somewhat parallel to themounting portion 62 and has an indentation 92 at one end for receivingand engaging the output conductor 24 and thereby conducting an outputsignal to the output conductor 24. Additionally, it should be understoodthat the other five collector units will each have a similar connectionfor engaging a selected one of the output conductors 25-29.

A detection means upon which a respective ion beam impinges comprises anelectron multiplier connected to the frame 44. The multiplier 100 may,for example, be a Mullard B Series tube. As shown in FIG. 4, the ionbeam travels in the path of the arrow B and impinges on a detectingportion of the multiplier 100.

The inputs to the multiplier 100 are taken via conductors 110, 111 fromcontacts 114, 115, respectively, spaced from one another at the outerface of the body portion 46. Electrical contact is made with a pair ofbusbars 120, 121 by means of suitable contacts 124, 125. The busbars120, 121 are spaced and parallel to one another and to the path oftravel of the collector unit 40 so that electrical contact may bemaintained with terminals 114, 115 while the collector unit 40 is movedback and forth. The ends of the busbars 120, 121 are connected to thesupport blocks 20, 22, respectively, and are connected to a suitablesupply voltage for the multiplier 100 via conductors 128, 129. Theoutput end of the multiplier 100 is electrically connected to thecollector plate 70. Sir

nals from the multiplier are transmitted from the collector plate 70 viathe output conductor 24.

As already mentioned, the collector units are similarly constructed anddiffer only in the. means for conducting an electrical signal to theoutput conductors 24-29. As shown, the collector unit 40 is adapted totransfer a signal to output conductor 24, collector unit 41 is adaptedto transfer an output signal to output conductor 25, and collector unit42 is adapted to transfer an output signal to the conductor 26. Also,all three collector units 40, 41, 42 receive the appropriate inputpotential from the busbars 120, 121.

In operation, if the collector arrangement is intended to be permanentlymounted within a mass spectrometer, suitable adjustment means may beprovided as described in the British specification No. 957,117. If thecollector arrangement is intended to be inserted and removed from a massspectrometer, a suitable template can be made on a previously exposedand developed photographic plate or on a fluorescent plate with a longdecay time. The respective positions of the individual collector unitsmay be chosen to correspond with the position of peaks appearing on thetemplate and the collector arrangement may then be inserted into themass spectrometer to electrically detect ions in a predetermined portionof the mass spectrum.

An alternative form of the present invention is shown in FIG. 5. Thisarrangement similarly has a support plate 130 having entrance slots 132,133 aligned end-to-end olngitudinally near an edge of the support plate130. The support plate 130 also includes adjustment slots 135, 136 toprovide room for movement of clamps 138, 139 slidably connected to thesupport plate 130. The clamps 138, 139 hold ion collectors 142, 143,respectively, arranged adjacent the entrance slots 132, 133,respectively, each for receiving an oncoming ion beam in a predeterminedrange of the mass spectrum. The ion collectors 142, 143 are ceramictubes which are lined with a suitable conductive, collecting metalmaterial. Upper portions of the ion collectors 142, 143 are cut away toprovide concave surfaces oriented toward the entrance slots 132, 133.

The output from the ion collector 142 is taken via a conductor 146through a ceramic tube 147 connected to the support plate 130 by meansof a clamp 148. An output conductor 149 from the ion collector 143 andthe conductor 146 both pass through twin bores in a ceramic tube 150indicated in dotted lines connected to the support plate 130 by means ofa clamp 152 also indicated in dotted lines. The conductors 146, 149 thenproceed to contacts 154, 155 respectively mounted on slides 157, 158,respectively, slidably arranged on a ceramic support rod 159. Theoutputs from the ion collectors 142, 143 are ultimately taken from thecontacts 154, 155.

As with the first form of the present invention, it may be preferable toprovide means for moving ion collectors 142, 143 to desired locationswith the entire collector arrangement mounted within an evacuatedportion of a mass spectrometer.

With both forms of the invention described in detail, it will beapparent to a person of ordinary skill in the art how many individualcollectors should be used in the analysis of a particular substance andwhat portions of the mass spectrum should be studied. As describedabove, the individual collector positions may be selected either beforeexposure, or if external adjustment means is employed, adjustments mayadditionally be made during exposure.

Although the invention has been described in its preferred forms with acertain degree of particularity, it is understood that the presentdisclosure of the preferred forms has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. A mass spectrometer for analysis of material comprising:

(a) an ion source for producing ions of a material to be analyzed, theions established in a beam along a path;

(b) magnetic deflection means disposed near the path of the ion beam fordeflecting the ions into a plurality of ion beams;

(c) a collector structure including:

a plurality of collector assemblies;

a base plate having at least one elongated ion beam opening therein andparallel track means for supporting said plurality of collectorassemblies;

fastener means associated with each said collector assembly for securingsaid associated assembly to said track means;

each assembly including a generally U-shaped frame member having a baseconnected to said fastener means, a body portion, and an upper armportion;

a plurality of output conductors each connected to a different assemblyfor transmitting signals from the assemblies;

each of the assemblies also includes a collector secured to the upperarm and a connection connecting the collector to its output conductor;

each assembly further includes a mechanism sensitive to ion bombardmentconnected to the collector for emitting signals when struck by ions thathave passed through said opening;

4 said plurality of output conductors adapted to be coupled to anindicator means for providing an output indication representative ofsaid emitted signals.

2. The apparatus of claim 1 wherein the collectors are multiplier tubes.

3. The apparatus of claim 1 wherein the collectors each include anon-conductive tube lined with a metal conductive material.

4. An electrical collector mechanism for a mass spectrometer comprising:

(a) a base plate having elongated slits and at least one parallelelongated ion beam transmitting opening;

(b) a plurality of collector assemblies each secured to the base plateby a plurality of fasteners passing through said slits;

(c) each assembly including a generally U-shaped frame member having abase connected to said fasteners, a body portion, and an upper armportion;

(d) a plurality of output conductors each connected to a difierentassembly for transmitting signals from the assemblies;

(e) each of the assemblies also includes a collector secured .to theupper arm and a connection connecting the collector to its outputconductor;

(f) each assembly further includes a mechanism sensitive to ionbombardment connected to the collector for emitting signals when struckby ions that have passed through said opening;

(g) said plurality of output conductors adapted to be coupled to anindicator means for providing an output indication representative ofsaid emitted signals.

5. The structure of claim 4 wherein each collector assembly includes anelectron multiplier for receiving an ion beam.

6. The collector mechanism of claim 4 wherein each of the assembliesincludes a connector in sliding engagement with its associated outputconductor whereby to maintain electrical contact in any adjustedposition.

7. The collector mechanism of claim 4 wherein each of the assembliesincludes a connection removably secured to the balance of the assemblyat a selected location in alignment with its output conductor and theassemblies are identical except for the selected position of theconnection.

8. The mechanism of claim 4 wherein each mechanism sensitive to ionbombardment includes a non-conductive tube lined with a metal conductivematerial.

9. An electrical collector for a mass spectrometer comprising:

a plurality of collector assemblies;

a base plate having at least one elongated ion beam opening therein andtrack means generally parallel to said beam opening for supporting saidplurality of collector assemblies;

fastener means associated with each said collector assembly for securingsaid associated assembly to said track means;

each assembly including a generally U-shaped frame member having a baseconnected to said fastener means, a body portion, and an upper armportion;

a plurality of output conductors each connected to a diflerent assemblyfor transmitting signals from the assemblies;

each of the assemblies also includes a collector secured to the upperarm and a connection connecting the collector to its output conductor;

each assembly further includes a mechanism sensitive to ion bombardmentconnected to the collector for emitting signals when struck by ions thathave passed through said opening;

said plurality of output conductors adapted to be cou pled to anindicator means for providing an output indication representative ofsaid emitted signals.

10. The apparatus of claim 9 wherein the collectors each include anon-conductive tube lined with a metal conductive material.

11. The mechanism of claim 9 wherein each mechanism sensitive to ionbombardment is an electron multiplier.

12. An electrical collector as defined in claim 9 wherein said trackmeans is an elongated track means situated in parallel relationship withrespect to said elongated ion beam opening.

13. An electrical collector as defined in claim 12 wherein said trackmeans includes a pair of elongated track means situated in parallelrelationship with respect to each other.

14. An electrical collector as defined in claim 12 wherein said trackmeans is defined by at least one elongated slit extending through saidbase plate and being generally parallel to said ion beam opening, andeach said collector assembly is secured to said base plate by saidassociated fastener means extending through said elongated slit.

References Cited UNITED STATES PATENTS 2,566,037 8/1951 Shewell 2504l.92,854,583 9/1958 Robinson 2504l.9 3,240,931 3/1966 Wiley et al 2504l.9

FOREIGN PATENTS 957,117 5/1964 Great Britain.

WILLIAM F. LINDQUIST, Primary Examiner

